update 0347-top-k-frequent-elements.scala (better memory usage)

Author: krishna1m

scala/0347-top-k-frequent-elements.scala

@@ -1,19 +1,29 @@
-import scala.collection.mutable.{HashMap, PriorityQueue, ListBuffer, ArrayBuffer}
-
+import scala.collection.mutable.{Map => MMap}
 object Solution {
-    def topKFrequent(nums: Array[Int], k: Int): Array[Int] = {
-        val map = getNumCountMap(nums)
-        val arr = Array.fill(nums.length + 1)(ListBuffer[Int]())
-        map.foreach{case (num, count) => arr(count) += num}
-        arr.reverseIterator.flatten.take(k).toArray
+  def topKFrequent(nums: Array[Int], k: Int): Array[Int] = {
+    // number -> count
+    val numberCountMap: MMap[Int, Int] = MMap[Int, Int]()
+    def traverseAndUpdateMap(rem: Array[Int]): Unit = {
+      if(rem.isEmpty) ()
+      else {
+        numberCountMap.updateWith(rem.head) {
+          case Some(value) => Some(value + 1)
+          case None => Some(1)
+        }
+        traverseAndUpdateMap(rem.tail)
+      }
     }
 
-    def getNumCountMap(nums: Array[Int]): HashMap[Int, Int] = {
-        val map = HashMap[Int, Int]()
-        nums.foreach(num => {
-            map(num) = map.getOrElse(num, 0) + 1
-        })
-        
-        map
+    implicit val ordering: Ordering[(Int, Int)] = {
+      Ordering.by[(Int, Int), Int](_._2).reverse
     }
-}
+
+    traverseAndUpdateMap(nums)
+
+    numberCountMap
+      .toArray
+      .sorted
+      .take(k)
+      .map(_._1)
+  }
+}